1. Field of the Invention
The present invention relates to quartz oscillators used for oscillating devices including a quartz thin-film vibrator, and particularly relates to a quartz oscillator including a quartz filter and to a method for manufacturing the quartz oscillator.
2. Description of the Related Art
A quartz oscillator is generally referred to as one having a quartz blank designed on the basis of the required performance, thin-film electrodes provided on the surfaces of the quartz blank, and a retainer including a thin supporting plate functioning as both mechanical support and an electrical lead, wherein the quartz blank and the thin-film electrodes are stored in the retainer in a sealed manner. On the other hand, a quartz filter is a device having a function of extracting required frequency components from various signal components and attenuating undesired frequency components. Among such filters, an MCF (Monolithic Crystal Filter), which includes two electrodes provided on a crystalline wafer and which has filter characteristics based on a combination of two vibration modes, is widely known. Since the present invention generally relates to quartz oscillators, structures thereof, and manufacturing methods thereof, the term quartz oscillator includes quartz filters and is used in a broad sense herein.
Quartz oscillators are used as important devices essential to information communication because of their high stability. Recently, with the development of communication satellites and mobile phones, high performance and miniaturization have been strongly required.
Depending on the above requirements, various methods have been proposed. A method for manufacturing a monocrystalline quartz thin-film by a sol-gel process is disclosed in Japanese Unexamined Patent Application Publication No. 8-157297, and a method for processing a quartz blank is disclosed in Japanese Unexamined Patent Application Publication No. 5-327383. In Japanese Patent Application No. 2000-270300, the inventors have proposed an atmospheric pressure vapor phase epitaxy (AP-VPE) method in which epitaxial growth is performed on a base by the reaction of silicon alkoxide with oxygen in atmospheric pressure without using a vacuum apparatus.
Since the frequencies used in mobile communication systems have reached the GHz band, the quartz oscillators used therein should generate higher frequencies.
Since the oscillating frequency of a quartz oscillator is inversely proportional to the thickness of the quartz blank, the quartz blank should have a small thickness. However, it is difficult to achieve a quartz blank having a thickness of 40 xcexcm or less by current processing methods. Thus, the oscillating frequency of mass-produced quartz oscillators has not exceeded about 40 MHz when using the fundamental wave.
In order to increase the frequency, it is necessary to employ a processing method such as wet etching or dry etching. However, when the etching rate is reduced to improve the control of the thickness, there is a problem in that it takes a long time to achieve a desired thickness because the large quantity of quartz chippings formed by etching needs to be removed.
In order to solve the above problem, the inventors have developed an atmospheric pressure vapor phase epitaxy (AP-VPE) method in which epitaxial growth is performed on a base by the reaction of silicon alkoxide with oxygen in atmospheric pressure without using a vacuum apparatus, and have made a patent application, filed as Japanese Patent Application No. 2000-270300.
Accordingly, it is an object of the present invention to provide a quartz oscillator including a base and a quartz thin-film formed on the base by the above-mentioned method and to provide a method for manufacturing the quartz oscillator.
In order to achieve the above object, according to the present invention, a quartz oscillator includes a base having a crystal face, a quartz thin-film formed on the face of the base by epitaxial growth under atmospheric pressure, a vibrating reed portion formed by processing the quartz thin-film, and excitation electrodes for exciting the vibrating reed portion.
In the quartz oscillator, the base is one selected from the group consisting of a single-element semiconductor, a compound semiconductor, and an oxide.
In the quartz oscillator, the single-element semiconductor is one of Si and Ge, the compound semiconductor is one selected from the group consisting of GaAs, GaP, GaN, ZnS, and ZnSe, and the oxide is one selected from the group consisting of Al2O3, ZnO, MgO.
The quartz oscillator further Includes a semiconductor circuit provided at an area of the base where the vibrating reed portion is not situated, wherein the base is a semiconductor crystal.
In order to achieve the above object, according to the present invention, a method for manufacturing a quartz oscillator includes the steps of preparing a crystalline wafer for a base, epitaxially growing a quartz thin-film on the base, forming a vibrating reed portion by processing the quartz thin-film and the base, and providing excitation electrodes for exciting the vibrating reed portion.
In order to achieve the above object, a method for manufacturing a quartz oscillator indudes the steps of preparing a crystalline wafer for a base, epitaxially growing a crystalline layer on the crystal of the base, epitaxially growing a quartz thin-film on the crystalline layer, forming a vibrating reed portion by processing the quartz thin-film, the crystalline layer and the base, and providing excitation electrodes for exciting the vibrating reed portion.
In the method for manufacturing a quartz oscillator, the crystalline wafer has a buffer layer disposed thereon and the vibrating reed portion is disposed on the buffer layer.
The method for manufacturing a quartz oscillator further includes the step of processing the base after epitaxially growing the quartz thin-film on the base, wherein a portion or all of the processed base has a thickness of several hundreds of microns.
The method for manufacturing a quartz oscillator further includes the step of partly removing the quartz thin-film or the base by machining or chemical-processing after forming the quartz thin-film by epitaxial growth.
In order to achieve the above object, a quartz oscillator includes a base having a recessed portion provided on one face thereof by processing to have a inverse mesa shape, a quartz thin-film formed on the other face of the base by epitaxial growth to have a thickness of 10 xcexcm or less, a vibrating reed portion, and excitation electrodes for mechanically supporting the quartz thin-film and for vibrating the vibrating reed portion.
As described above, according to the present invention, the quartz thin-film is directly formed on the base comprising a single-element semiconductor such as Ge and Si, a compound semiconductor, or an oxide by epitaxial growth. Thus, the quartz thin-film can be processed precisely and can be made extremely thin, so that quartz oscillators having a resonant frequency of at least 100 MHz and including a quartz thin-film with a thickness of 20 xcexcm or less can be readily manufactured, which has not been achieved conventionally.
Furthermore, the quartz thin-film has an extremely small thickness and is easy to handle.
In a method for manufacturing a quartz oscillator according to the present invention, ft is not necessary to remove quartz chippings during the etching step, whereas their removal has been required in conventional methods. Thus, the manufacturing cost can be reduced.
According to the present invention, a semiconductor circuit, which is used as an oscillating circuit, can be provided on the base of a quartz oscillator, that is, a quartz oscillator including an oscillating circuit In an integrated manner can be provided. When the quartz oscillator is used in a quartz filter, an integrated filter that has a preamplifier or a buffer amplifier can be provided in an integrated manner. Such an integrated filter has filter characteristics, which are resistant to being disturbed by external circuits. Furthermore, impedance matching in the integrated filter is easy.